Method for producing strip conductors having uniformly insulated edges



April 14, 1964 c. F. MANNING ETAL METHOD FOR PRODUCING STRIP CONDUCTORS HAVING UNIFORMLY INSULATED EDGES Filed 001:. 6, 1959 2 Sheets-Shet 1 FLASH MELTING AT ROLLING OF ANOD'C EDGES 0 RAPIDLY HEATED apaes MOVING STRIP OF MOVING STRIP INVENTORS CL4RE/VCE F." MANN/N6 (J HN 374LEY 7710/14/43 E: LEW/5 April 14, 1964 MANNING ETAL HAVING UNIFORMLY INSULATED EDGES Filed Oct. 6, 1959 2 Sheets-Sheet 2 ?Tg- 4 U 5 FT 1 6 E 7 INVENTORS CL ARENCE F: MA'NN/NQ JOHN STALE'Y THO/M45 E. LEW/S ATTORNEY C. F. 3,128,547 METHOD FOR PRODUCING STRIP CONDUCTORS United States Patent M 3,123,547 METHGD FOR PRGDUCING STRIP CONDUCTORS HAVING UNIFGRMLY INSULATED EDGES Clarence F. Manning, Manahin, John Staley, Richmond,

and Thomas E. Lewis, Chesterfield County, Va, assignors to Reynolds Metals (Iompany, Richmond, Va., a

corporation of Delaware Filed Oct. 6, 1959, Ser. No 846,530 Claims. (Ci. 29-527) This invention relates to a new and improved method for producing insulated strip conductors suitable for fabrication into electrical coils. It is particularly well suited for the treatment of thin metal conductors, formed of aluminum foil and which are to be insulated by the deposition of an anodic coating thereon.

As is known, the elongated strip of foil which is to serve as the conductor is normally formed by slitting of an elongated sheet of commercial width and with the slitting taking place along parallel lines which define the lateral edges of the conductor. Experience has shown that, regardless of the sharpness of the slitting apparatus, these lateral edges, when considered in the microscopic dimensions applicable to anodic coating procedures, are found to have irregular or burred surfaces, as, for example, sharp points, corners, and various other forms of nonsyrnmetry. When subjected to an anodizing treatment without intermediate modification of these slitted edges, such a strip is unable to take a uniform deposition of anodic coating over its surface and edges. Various methods for modifying the edge portions of such strips prior to the anodizing treatment have been suggested, as, for example, the brushing of the irregular edges or the longitudinal folding of the slitted strip so as to provide a thickened conductor having rounded edges. The present invention makes available still another solution to this problem and in which the slitted edges are rendered substantially smooth by a melting of the edge followed by a reshaping thereof. We now have found that, by following the practices hereinafter set forth, an improved strip conductor having uniformly anodically insulated edges may be produced.

One object of our invention is to provide an improved process for forming insulated strip conductors.

Another object is to provide an improved method for reshaping the slitted edges of a strip conductor prior to deposition of an anodic coating thereover.

Another object is to provide an improved method for melting and rolling the slitted edges of an aluminum strip conductor.

Other objects and advantages will become more apparent when the following description is considered in conjunction with the accompanying drawings showing diagrammatically the several steps of our preferred method.

In the drawings,

FIG. 1 is a flow diagram showing the sequence of steps employed, with the dotted lines indicating a discontinuity of continuous processing.

FIG. 2A represents a diagrammatic arrangement of conventional apparatus suitable for carrying out the melting and rolling steps of processing.

FIG. 2B represents a diagrammatic arrangement of conventional apparatus suitable for carrying out the anodic coating step of processing.

FIG. 3 represents a suitable arrangement of electrodes in an atomic-hydrogen arc welding zone of conventional apparatus adjacent which the edge of the slitted strip rapidly moves.

FIG. 4 represents a highly magnified microphotograph of an edge portion of a cross section at the slitted edge 3,128,547 Patented Apr. 14, 1964 of a conventional aluminum foil strip of 0.008" thickness, showing the burred irregular edge after a very careful slitting of the strip.

FIG. 5 represents the edge portion of the strip shown in EEG. 4 following the melting step of operation.

FIG. 6 represents the edge portion of the strip shown in FIG. 5 following the rolling step of operation and prior to the deposition of the anodic coating and FIG. 7 represents the edge portion of the strip shown in FIG. 6 and following the deposition of the anodic coating.

In carrying out our invention, we prefer to subdivide our process into three discontinuous phases, although in its broader aspects the moving strip of material may move continuously if desired. Since the anodic coating phase is relatively slow with respect to the slitting phase, and is particularly slow with respect to the melting and rolling phase, it has been found normally desirable to interrupt the continuous movement of the strip at the points indicated by dotted lines in the flow diagram of FIG. 1. In general, the process of the invention comprises the formation of large rolls of relatively narrow strip material by means of the slitting of a wide sheet of material; the passage of the rolled strip under tension rapidly through the melting and reshaping zones; the passage of the rewound strip under tension slowly through the anodizing zone; and the rewinding of the finished insulated strip preparatory to later fabrication of the same into electrical coils. While the rolls of slitted strips may be formed from thin sheets of various metals, we prefer to employ aluminum foil as the stock material, the initial thickness of the foil being within the range of 0.00017 to 0.060

inch. Normally, the insulating anodic coating will have a thickness of about 0.0001 to 0.001 inch. Thus, by means of the invention, extremely thin insulated conductors may be fabricated into coils, windings and the like (all herein designated as coils) for use in electrical apparatus wherein space limitations are significant.

Referring now to FIG. 4, a typical edge 11 of a conventional strip 10 of foil cut by a slitting operation will be seen to have an uneven shape including such irregularities as sharp corner 12, sharply convergent recesses 13, 14, sharp projections 15, 16 and the like. It will be understood that the second irregular edge 17 of the same strip or sheet is of substantially the same configuration as edge 11 and is parallel thereto. When such a sheet has an anodic or other insulation coating applied thereto, only an inadequate amount is deposited on the surface at the most marked of such irregularities. We have now discovered that this inherent disadvantage of the slit sheet stock may be overcome by melting the irregular edge to a somewhat convex protruding from wherein surface tension forces causes the irregularities to disappear, as indicated generally in FIG. 5; followed by a rolling of the melted edges to provide a strip of substantially uniform transverse thickness as indicated generally in FIG. 6; followed by a conventional anodic or organic or other insulating coating to provide a conductor uniformly insulated at its edges, as indicated generally in FIG. 7.

Referring now to FIG. 2A, a roll of previously slitted aluminum foil, having the above-described irregular edges '11 and i7, is suitably mounted so as to pass a moving web of material horizontally through edge melting, and edge rolling apparatus in sequence. The web with its edges treated in the manner later to be described is then rewound upon a conventional spool 20 driven in a suitably controlled manner by any conventional driving means, such as electric motor 21. It will be understood that in the practice of our invention the moving web remains under tension so as to be moved at a uniformly relatively high speed for this purpose the web is fed into the flash melting furnace 22'. between guide rollers 23, 24 of any conventional type serving to position the edges of the web at the proper location with respect to the furnace electrodes.

Upon leaving the furnace, the web rapidly moves between conventional metal working rolls 25, 26 driven by any suitable means (not shown) at a speed commensurate with the rolling action required. If desired, the web may also be subjected to a cooling action by means of any conventional apparatus, not shown, as for example, a blower gently moving a stream of refrigerated air against the moving web. Upon leaving the rolls, the web is then wound upon the spool 20.

Reference now is made to FIG. 3 showing a diagrammatic representation of one side section of the flash melting furnace 22. We prefer to employ a conventional atomic-hydrogen arc welding furnace wherein an AC arc is maintained between two tungsten electrodes in an atmosphere of hydrogen. As is known, the molecules of hydrogen separate into their component parts-atorns -as the gas passes through the are from the jets or orifices around the tungsten electrodes. The gas in the atomic state is readily displaced with molecular hydrogen under a slight pressure and is edged out of the arc. When out of the influence of the arc, the hydrogen atoms recombine into the normal molecule and in so doing, give up their heat of dissociation. It is this heat which we employ to melt the edges of the moving strip; and since the degree of applied heat may be readily controlled both by adjusting the position of the moving strip with respect to the arc and by regulating the speed of the moving strip; and further, since the melting takes place in an atmosphere of hydrogen where oxidation does not occur, we thus are enabled by our process to produce a strip having edges particularly suitable for a later anodic or other treatment.

Furnace 22 may comprise a compact box-like structure of refractory material having a T-shaped slot 39 through which web 14% passes. An arcuate cavity may be provided at each side of the slot with a pair of tungsten electrodes 31, 32 and 33, 34 disposed therein. Hydrogen gas under a slight superatmospheric pressure may be supplied to the cavities as illustrated by the concentric apertures 35, 36 surrounding the electrodes in FIG. 3. A current flow of 75 amperes or less between the electrodes provides an are which disassociates sufficient hydrogen to heat a strip of aluminum foil moving at not less than 30 feet per minute, sufficiently to melt the irregular edges in accordance with the invention. Thus, a given portion of an edge of the conductor does not remain in the region of intense heat for more than a fraction of a second. It will be understood that the distance between edge 17 of the web It and the are, as well as the speed at which the web is moved, are both related to the thickness of that web, the smaller the thickness, the faster the speed and the greater the distance between the edge of the web and the arc.

It has been found that upon being subjected to the flash heating in the furnace, the edges of the moving web rapidly melt and under the influence of surface tension forces form a somewhat convex protruding nonsymmetrical shape as indicated in FIG. with the greater portion of the protrusion below the center line of the web. In being thus modified, the marked dissimilarities of the slitted edges as seen in FIG. 4 disappear. The web preferably lies in a horizontal plane during the melting and rolling phases of treatment with the result that no material change in width of the conductor occurs when the modified edges are rolled.

Promptly after being melted and before the plastic edges can detach themselves, the web is moved between conventional foil working rolls 25, 2s whereupon the enlarged edges are reduced in size to form a web having a substantially uniform transverse thickness as seen in FIG. 6. During this rolling operation, the smooth heated edges of the strip retain their smooth configuration. As will be apparentto those skilled in the art, web cooling means may be provided between the rolls and the winding spool, or at both locations, should this be desirable. Following the rolling, the web is then wound upon spool 2%.

Considering now FIG. 23, an apparatus for applying an anodic insulating coating to the above described strip conductor, is diagrammatically illustrated. A previously loaded spool 29 is suitably mounted with respect to guide roller til adjacent an anodizing treatment tank 41. This tank may contain an electrolytic bath 42 which for purposes of illustration may comprise an anodizing solution consisting of an aqueous solution of sulfuric acid at a concentration of about 15-18% and held at a temperature of about 70 degrees F. The uninsulated web 14 leaving guide roller 44) passes through the bath in contact with a suitable electrolytic roller 43 which may have suitable insulation on the sides and be suitably driven and provided with transverse shaft members, not shown, mounted in appropriate insulating bearings in the sides of the tank. A slip ring connection 44 may connect the roller to the positive terminal of an electrical circuit while the negative terminal of the same circuit may be connected to a series of spaced cathode terminals 45 disposed in the bath beneath the moving web it). As an alternative, the positive lead may be attached to the moving web 1% itself rather than to the electrolytic roller, but in general this arrangement adds to heat losses. Depending upon the thickness of insulation desired, as well as upon current density and the nature of the electrolytic bath, the moving web may remain in the bath from about one-sixth to 25 minutes, and preferably for about three minutes.

While in the bath, the edges of the previously melted and rolled strip conductor, as well as one or both sides of the conductor (depending upon the type of roller 43), are coated with an anodically deposited insulating film 43 which in the form illustrated is an aluminum oxide. As noted in FIG. 7, this coating is of substantially uniform thickness and uniform insulating value due to the ability of the edges of the treated strip to receive the electrically deposited coating in a uniform manner.

Upon leaving the bath by passing over the guide roller 47, the insulated web It) may, if desired, receive conventional rinsing, sealing, supplemental coating, or other treatments not illustrated, after which it is wound upon a winding spool 35a driven by any suitable driving means 46, or when such supplementary treatments are not desired, may be wound directly upon that spool after leaving the tank. The completed conductor may thereafter be passed from spool 45a into appropriate winding apparatus, forming no part of this invention, for fabrication into electrical coils.

It thus will be seen that our invention teaches a method of efficiently forming an improved anodic or other insulated strip conductor from an originally uninsulated strip having irregular edges and within the passage of the stock material may move through the several phases of treatment at varying speeds. By suitably regulating the speed of driving means 21 and 46, the stock material may be passed through the treating phases at speeds which provide the most eflicient treatment.

Having thus described our invention by a particular embodiment thereof, it will be understood that we do not wish to be limited thereto, since many modifications may be made; and we therefore contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope-of our invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

l. The method of forming an insulated strip conductor comprising, rapidly moving an uninsulated conductor having burred edges through a heating zone to melt said burred edges and cause surface tension to form protruding rounded edges thereon, rolling said rounded edge conductor to provide a substantially uniform thickness transversely thereof, and thereafter insulating said conductor by depositing an insulating coating thereon.

2. The method of claim 1 wherein each of said burred edges is separately and simultaneously melted into a rounded configuration.

3. The method of claim 1 wherein said conductor is moved through said heating zone under tension.

4. The method of claim 1 wherein said conductor moves through the heating zone and the rolling operation at the same speed.

5. The method of claim 1 wherein said conductor moves through the heating zone and the rolling operation at the same speed and is moved through the insulating operation at a lesser speed.

References Cited in the file of this patent UNITED STATES PATENTS 1,989,796 Firth Feb. 5, 1935 2,125,173 Kinzel July 26, 1938 2,185,496 Brown Jan. 2, 1940 2,266,552 Jones Dec. 16, 1941 2,306,370 Anderson Dec. 29, 1942 2,423,188 Herbst July 1, 1947 2,479,353 Hansell Aug. 16, 1949 2,501,616 Robinson Mar. 21, 1950 2,619,881 Dudley Dec. 2, 1952 2,971,294 Hohmann et a1. Feb. 14, 1961 3,055,241 Hedgecock et a1 Sept. 25, 1962 

1. THE METHOD OF FORMING AN INSULATED STRIP CONDUCTOR COMPRISING, RAPIDLY MOVING AN UNINSULATED CONDUCTOR HAVING BURRED EDGES THROUGH A HEATING ZONE TO MELT SAID BURRED EDGES AND CAUSE SURFACE TENSION TO FORM PROTRUDING ROUNDED EDGES THEREON, ROLLING SAID ROUNDED EDGE CON- 